The invention concerns a method for exactly determining the top dead centre (TDC) of an internal combustion engine from the pressure curve inside the cylinder. The top dead centre (TDC), more exactly the point-at the end of the compression phase, is known to be an important value in the cycle of a reciprocating combustion engine, as for calculating the cylinder power output for example. Determining it directly involves much effort and is relatively inaccurate, especially on multicylinder engines. Accordingly determining the TDC from the pressure curve inside the cylinder has already been suggestedxe2x80x94by K. Wehner, xe2x80x9cBestimmung des dynamischen OT aus dem Zylinderinnendruckverlauf von Verbrennungsmotorenxe2x80x9d, IBZ e.V.; (Innovation and Education Centre, registered association in Germany; published in 1996). This known method compares the pressure curve inside the cylinder calculated with the equation of the ideal adiabatic changes of state with the measured curve; the parameters of the calculated curve are then varied iteratively till adequate agreement with the measured curve is attained. As the final step the TDC calculated with the approximation procedure is then taken over into the measured curve. This method involves a considerable amount of calculation firstly, while secondly it does not take into account the actual conditions during the operation of the engine, such as heat losses of the gas, gas losses (i.e. leakages) and deformations of the engine. Though these errors can be compensated in part with empirical values or mathematical models, this then calls for still more calculation.
The purpose of the invention therefore is to provide a method for determining the TDC from the pressure curve inside the cylinder, demanding relatively little calculation and taking into account the actual engine behavior.
Provided there is a properly trained knowledge-based system, then TDC detection and possibly different engine-specific parameters demand only one measurement of the pressure curve inside the cylinder and input of the pressure values into the knowledge-based system, which has learned to allocate the right TDC to them.
Thus the structure of the knowledge-based system and the training effort can be reduced with engines of one type, such as large-bore diesel engines having the same engine-specific parameters, by using only the pressure curve inside the cylinder for TDC detection in the trained system. To verify whether the knowledge-based system is adequately trained it has proved efficacious to subdivide the quantity of correlated cylinder pressure and TDC time pairs from direct measurement into subquantities, of which one at least is used to check the generalization capability of the knowledge-based system.
The accuracy of the training and TDC detection in xe2x80x9coperationxe2x80x9d can be raised by defining the course of the pressure inside the cylinder with a time lag in relation to the TDC during the system training, so that the TDC falls into the compression phase and the knowledge-based system is trained for a TDC in this phase, and this deliberate systematic error is then cancelled by the unchanged, trained, knowledge-based system. Furthermore TDC detection by the knowledge-based system is improved if the electrical properties of the measuring arrangement, such as the filter frequency, when recording the pressure curve inside the cylinder and the direct TDC time measurement on the one hand, and on the other hand the engine-specific parameters during operation, i.e. at TDC time detection in unknown operating states and/or untrained machine-specific parameters, are made as identical as possible.
Calculation of the cylinder output may be simplified by combining the pressure curve inside the cylinder with a linear scale in degrees of crank or crankshaft angle (xc2x0 CA), referenced to the TDC time determined from the pressure in the cylinder. If such a simplification is too inaccurate, the linear scale may be adapted to the shape of the actual curve over the time interval with the help of another knowledge-based system.
The meanings and scope of some of the terms employed in these documents will now be defined:
xe2x80x9cPressure curve inside the cylinderxe2x80x9d includes not only the direct measurement of this variable but also other measurable variables depending on it, such as the elongation in a cylinder head bolt (EP-A-0170.256 corresponding to U.S. Pat. No. 4,606,312) or in the cylinder liner (EP-B-0671.618) and the pressure between cylinder head and nut (U.S. Pat. No. 5,179,857) or a length change between two walls of the cylinder head (EP-A-0175.449 corresponding to U.S. Pat No. 4,601,196).
xe2x80x9cDifferent operating pointsxe2x80x9d are obtained by varying the revs per minute, fuel mixture, injection timing, ignition timing, load, charging pressure and/or temperature for example, whereby the temperature is always measured in the equilibrium state, i.e. after starting. Other operating states result from the number of operating hours logged by the particular engine.
xe2x80x9cKnowledge-based systemsxe2x80x9d are artificial neural networks (NN), neuro-fuzzy systems or fuzzy systems for instance. With fuzzy systems the process knowledge is put in selectively, whereas with neuro systems the system must acquire the process knowledge itself from the training phase. The xe2x80x9cengine-specific parametersxe2x80x9d include geometric dimensions like cylinder bore and piston stroke, as well as compression and possibly other characteristic data of an engine type.
The invention will now be described in more detail with reference to a typical embodiment and the drawing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.